Diarrhea is the second leading cause of death among children less than five years old, causing about 2 million deaths annually. A meta-analysis of studies on handwashing with soap from low-, middle-, and high-income countries estimated a summary diarrhea risk reduction of 47%. Despite the proven health benefits of handwashing, data from numerous settings confirm that individuals do not practice good hand hygiene at the appropriate times. It is critical to identify which individual-level factors are conducive to adoption of improved hand hygiene in response to handwashing promotion. We hypothesize those mothers with acutely ill children will have heightened perceptions of disease risk and will, therefore, show greater receptivity to a message encouraging handwashing behavior as a disease risk reduction strategy. Therefore, we propose to examine whether mothers whose children are currently suffering from diarrhea are more likely to improve handwashing behavior following a handwashing promotion intervention than are mothers of children who are currently well. To achieve this specific aim, we will conduct a 2x2 factorial randomized controlled trial in New Delhi, India in which we will enroll 400 households of children <2 years old. Of these, 200 will be households of children with acute diarrhea and 200 will be households of children who are well. From each group, we will assign 100 households to intensive handwashing promotion and 100 households to continue their usual hand hygiene practices (control). We will measure handwashing behavior during the acute diarrhea episode and again several weeks following resolution of the diarrhea using an innovative method consisting of motion sensors embedded in soap, which provide information on the number of times soap is used in the time period of interest without having a human observer present. The soap with motion sensor provides an objective measure of soap use and overcomes the reactivity that has been shown to occur in response to the presence of a human observer of handwashing behavior. In addition to this methodological innovation, the proposed study is conceptually novel. There is no information from published randomized controlled trials about whether risk perception is a motivating factor for the adoption of improved handwashing behavior. Such information will substantively inform future research on the decision-making processes involved in good hand hygiene and guide handwashing promotion programs in resource-poor countries where handwashing with soap at scale promises to reduce substantially the morbidity and mortality from diarrhea. PUBLIC HEALTH RELEVANCE: When mothers and other household members improve handwashing with soap, children suffer substantially fewer episodes of diarrhea, which is the second leading cause of death of young children worldwide. This innovative project aims to assess whether mothers of ill children are more likely to improve hand washing behavior compared to mothers of well children. Results from this study will be useful for international and civil society organizations worldwide that are trying to reduce the two million deaths from diarrhea occurring each year.